From its spiky Gothic cathedral to the elegant Pirelli Tower of the 1950s, Milan is a city filled with invention, which is fitting given that Leonardo da Vinci called it home. Its skyline has now been joined by the Bosco Verticale - the vertical wood or forest.

The idea of buildings that incorporate greenery is hardly new. Roof gardens were often featured in early Modernist buildings. The problem is that the plants are subject to heavy stresses of direct sun (or lack of it) and punishing winds as well as limited root space. In the early 21st century, French botanist Patrick Blanc pioneered the use of green walls using hydroponics which allows plants to mesh together and cover vertical walls. His work can be seen in One Central Park in Sydney, an apartment block whose windows are framed with foliage and flowers. The Bosco Verticale in Milan took a slightly different approach. The balconies of its two apartment towers are planted out with not only small shrubs but also a thousand trees, including oak, hazel, and fig, covering the equivalent of a 2.5 acre forest. Completed in 2014 and designed by Stefano Boeri, it quickly drew international acclaim and became the posterboy for green building principles.

The idea of using trees is logical. They screen the apartments from direct sunlight, filter out dust and pollution, actually create oxygen and provide habitat for wildlife. They've also helped create one of the most startling looking buildings this side of Babylon's Hanging Gardens, especially as the trees change colour with the seasons. It's become an icon for a new movement towards buildings that incorporate greenery. Singapore is a leader in this, adding to its garden city image, and aims to ensure, by 2030, that 80% of the state's buildings follow sustainable design principles, which includes abundant natural plantings on roofs and walls to lower energy costs. Other countries, from the UK to China, are following its lead, giving a new meaning to the concrete jungle. The benefits seem, at first, like a no-brainer. Bosco Verticale is estimated to use 7.5% less energy than a regular building with no greenery but some argue that it's no more than window dressing, as the extra cost in strengthening the structure to hold the huge weight of the plantings and the irrigation system outweighs the savings.

The Bosco Verticale may form an unusual addition to Milan's skyline today but it's likely that we'll soon view it as a pioneer as the taller structures in cities around the globe begin to actually form much of our natural landscape. As they say, mighty oaks from little acorns grow.